I think the practice in most cases in most states is that the buyer fills out Form 4473. And the dealer keeps that. And there it stops unless the gun is used in a crime. LE can go back to the manufacturer to find out where the gun was first shipped, then they can go to the dealer who first sold it, and he can produce the 4473. But in the meantime, that gun could have passed through numerous hands and the trail could go cold very quickly. Even if you knew who the dealer was, no way he would divulge that information to you as a private citizen. And of course, there are enormous numbers of guns having no 4473. As an individual, you will be SOL in trying to find an ownership history that way in virtually all cases. About the only exception would be if you bought a gun from the original owner. And also, in the case of a stolen gun, if the person from which the gun was stolen reported it, the national stolen gun registry could be checked. But unless you are a cop or know one well, that won't work either for you as a private citizen.